POTATO GROWERS need to maintain tight blight spray intervals throughout hot, dry weather, experts advise.

Even though recent settled weather has slowed development of the disease, rapid haulm growth of later planted crops has created the ideal microclimate for blight in many crops, warned the British Potato Council.

In particular, there was a flush of Smith Periods in East Anglia on July 8/9 and July 12/13, said Nick Bradshaw of the BPC’s blight advisory team.

“Blight inoculum is present in many areas albeit at very low levels and, although the disease is not developing at the moment, there is potential for a significant upsurge in activity if the weather breaks.”

“Thunderstorms are forecast for some areas and, if prolonged and significant, they could be the trigger for that increase in blight activity.”

Catchy showers and irrigation can both create the ideal microclimate within crops for blight development, agreed Dow AgroSciences principal biologist, Andy Leader.

“As the season progresses, lower night time temperatures between 10-15C and wet weather are optimal for infection of the tubers.”

Growers need to keep spray intervals tight and incorporate products with blight activity into their spray programme as soon as tuber initiation begins, he said.

He suggests using Electis (zoxium + mancozeb), which is recommended on all varieties of potato at spray intervals of 7, 10 or 14 days.

Growers can also check local blight pressure by logging on to the BPC’s blight mapping programme www.potato.org.uk/blight.